Certain devices such as wafer defect scanners, laser printers, document scanners, projectors and the like may employ a laser beam that scans across a flat surface in a straight line path. So as to effectuate this scanning, these devices employ tilting mirrors to deflect the laser beam. These tilting mirrors may be, or may include, Micro Electro Mechanical Systems (“MEMS”) devices. The laser light reflected by the tiling mirrors may be of a visible wavelength (for instance, the three red/green/blue colors) or of invisible wavelength (for instance, infrared light for 3-D imaging).
A conventional laser projection system 50 is now described with reference to FIG. 1. The laser projection system 50 includes a MEMS mirror 56, driven by a mirror driver 54, which implements the desired drive signal, whether it be high current (for electromagnetically driven MEMS mirrors) or high voltage (for electrostatically or piezoelectrically driven mirrors). The mirror driver 54 is controlled by a mirror controller 52 using a control signal 61 to control the waveform and the amplitude of the output analog drive signal 63.
The mirror controller 52, which may be incorporated within an application specific integrated circuit (ASIC), also functions to drive a synchronization signal 51 and clock signal 53 toward laser modulation logic 58, which sends a control signal 55 to a laser driver 60, which in turn generates a drive signal 57 that modulates the laser 62 in order to position the correct pixel in the laser beam 59 in correspondence to the movement of the MEMS mirror 56. This synchronization is critical, because if the driving of the laser 62 and the MEMS mirror 56 are not properly synchronized, the desired scan pattern is not formed, and the laser projection system 50 is considered to have malfunctioned.
However, it may be undesirable to send the clock signal 53 from the mirror controller 52 to the laser modulation logic 58 for a variety of reasons. For example, the mirror controller 52 and laser modulation logic 58 may be located within separate integrated circuits, and thus a pin or pad would be required to send and receive the clock signal 53 via such pin or pad. Particularly in the case of a laser projection system 50 used for forming high resolution images, the clock signal 53 is of a high frequency (on the order of GHz), and thus the sending of the clock signal 53 would consume power on the order of tens of milliwatts. This is undesirable for portable electronics applications which run on battery power, such as picoprojectors, smartphones, modular add on devices for smartphones, tablets, smartwatches, and the like.
Therefore, further development of circuits, techniques, and methods for synchronizing the mirror controller and laser modulation logic within a laser projection system is needed.